Add a ring buffer implementation.

This is intented to replace the pipe between the writer and reader 
threads. That way we can have a much better control of cancelation 
situations. Still to be optimized.

src/buffer.h

@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2007 Vreixo Formoso
+ * 
+ * This file is part of the libisofs project; you can redistribute it and/or 
+ * modify it under the terms of the GNU General Public License version 2 as 
+ * published by the Free Software Foundation. See COPYING file for details.
+ */
+
+#ifndef LIBISO_BUFFER_H_
+#define LIBISO_BUFFER_H_
+
+#include <stdlib.h>
+#include <stdint.h>
+
+/* 2 MB buffer */
+#define BLOCK_SIZE          2048
+#define BUFFER_SIZE         1024
+
+typedef struct iso_ring_buffer IsoRingBuffer;
+
+/**
+ * Create a new buffer.
+ * 
+ * The created buffer can be freed with free(3)
+ * 
+ * @return
+ *     1 success, < 0 error
+ */
+int iso_ring_buffer_new(IsoRingBuffer **rbuf);
+
+/**
+ * Write count bytes into buffer. It blocks until all bytes where written or
+ * reader close the buffer.
+ * 
+ * @param buf
+ *      the buffer
+ * @param data
+ *      pointer to a memory region of at least coun bytes, from which data
+ *      will be read.
+ * @param
+ *      Number of bytes to write
+ * @return
+ *      1 succes, 0 read finished, < 0 error
+ */
+int iso_ring_buffer_write(IsoRingBuffer *buf, uint8_t *data, size_t count);
+
+/**
+ * Read count bytes from the buffer into dest. It blocks until the desired
+ * bytes has been read. If the writer finishes before outputting enought
+ * bytes, 0 (EOF) is returned, the number of bytes already read remains
+ * unknown.
+ * 
+ * @return
+ *      1 success, 0 EOF, < 0 error
+ */
+int iso_ring_buffer_read(IsoRingBuffer *buf, uint8_t *dest, size_t count);
+
+/** 
+ * Close the buffer (to be called by the writer).
+ * You have to explicity close the buffer when you don't have more data to
+ * write, otherwise reader will be waiting forever.
+ */
+void iso_ring_buffer_writer_close(IsoRingBuffer *buf);
+
+/** 
+ * Close the buffer (to be called by the reader).
+ * If for any reason you don't want to read more data, you need to call this
+ * to let the writer thread finish.
+ */
+void iso_ring_buffer_reader_close(IsoRingBuffer *buf);
+
+/**
+ * Get the times the buffer was full.
+ */
+unsigned int iso_ring_buffer_get_times_full(IsoRingBuffer *buf);
+
+/**
+ * Get the times the buffer was empty.
+ */
+unsigned int iso_ring_buffer_get_times_empty(IsoRingBuffer *buf);
+
+#endif /*LIBISO_BUFFER_H_*/